Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $53.55   13.659%   $60.8644   $60.86   $60.85   $60.90  
  Purchase #2 $5.87   7.751%   $6.325   $6.33   $6.35   $6.30  
  Purchase #3 $199.59   10.577%   $220.7006   $220.70   $220.70   $220.70  
  Purchase #4 $131.44   7.298%   $141.0325   $141.03   $141.05   $141.00  
  Purchase #5 $135.53   11.357%   $150.9221   $150.92   $150.90   $150.90  
  Purchase #6 $201.91   4.663%   $211.3251   $211.33   $211.35   $211.30  
  Purchase #7 $191.72   6.401%   $203.992   $203.99   $204.00   $204.00  
  7 purchase totals = $919.61       $995.1617   $995.16   $995.20   $995.10